Topic 1: Key Concepts

• Eukaryotes - organisms made of eukaryotic cells with a nucleus and membrane
• Prokaryote - a single cell organism with no nucleus or membrane
• Animal Cells:

  • has subcellular structures
  • nucleus with genetic material (chromosomes)
  • cell membrane
  • mitochondria do respiration
  • ribosomes do protein synthesis
• Plant Cells:

  • has subcellular structures
  • ridged cell wall to support and strengthen plant
  • large vacuole containing cell sap that maintains internal pressure
  • chloroplasts have chlorophyll and photosynthesis
• Bacterial Cells:

  • has subcellular structures
  • chromosomal DNA has no nucleus
  • ribosomes
  • cell membrane
  • plasmid DNA used for evolution like drug resistance
  • flagellum helps with movement
• Sperm Cells:

  • long tail for swimming
  • lots of mitochondria to provide energy
  • acrosome contains enzymes that digest egg cell membranes
  • haploid nucleus
• Egg Cell:

  • nutrients in cytoplasm to nourish the embryo
  • haploid nucleus
  • membrane hardens when fertilised
• Ciliated Epithelial Cells:

  • line organ surfaces
  • cilia move substances in one direction along the surface
  • mucus in lungs moved to the throat via cilia
• Microscopes:

  • Resolution - how well a microscope distinguishes between two points that are close together (more clear/detailed)
  • Light microscopes - pass light through organisms to see large subcellular structures
  • Electron microscopes - higher magnification and resolution shows the internal structure of subcellular cells
• Magnification = Image size/Real size
• centimetre --10-> millimetre --1000-> micrometre --1000-> nanometre --1000-> picometre
• Enzymes:

  • biological catalysts
  • specific substrate molecule joins to the active site in a lock and key mechanism
  • rate of reaction affected by temperature, pH and concentration (optimum and denaturing factors)
• Light Microscope Practical:

  1. Use a pipette to add a drop of water on a clean slide so the thinly sliced organism can be secured with tweezers (add stain if colourless)
  2. Place a cover slip over the slide at an angle with a mounted needle and gently press down so there are no air bubbles
  3. Place the clip on the stage and select the lowest powered objective lens
  4. Use the coarse adjustment knob to move the stage up while looking through the eyepiece
  5. Adjust the focus using fine adjustment knot then use a ruler to measure the organism size to calculate the image real size
• Enzyme Activity pH Practical:

  1. Add a drop of iodine solution in each spotting tile
  2. Put a beaker of water on the tripod over the bunsen burner and try to make a constant 35'C
  3. Use a syringe to add 3cm3 of amylase solution and 1cm3 of buffer solution to a boiling tube then place it in the flask
  4. Add 3cm3 of starch solution to the boiling tube using a syringe then mix
  5. Take a sample every ten seconds and put it in a different spotting tile each time
  6. If iodine remains brown-orange then starch is no longer present
  7. Repeat with different pH values
• Chemical Reagents Practical:

  • Sugar – add Benedict’s reagent to solution and heat it until a coloured precipitate forms (higher concentration is red)
  • Starch – add iodine solution for a colour change from brown-orange to blue-black
  • Lipids – shake solution with ethanol for it to dissolve then add water so lipids will precipitate into a milky emulsion
  • Protein – add potassium hydroxide to make solution alkaline then add copper(II) sulfate which turns from blue to purple
• Calorimetry – measures energy contained in food

  1. Weigh a small amount of dry food then skewer it on a mounted needle
  2. Add set water volume to boiling tube
  3. Measure water temperature before and after burning the food under the boiling tube
  4. Energy = mass x temperature change x 4.2
  5. Energy per gram = food energy/food mass
• Cell Transportation:

  • Diffusion – the overall movement of particles from an area of higher concentration to lower concentration (cell membranes)
  • Active Transport – the movement of particles across a membrane against a concentration gradient using energy during respiration
  • Osmosis – the overall movement of water molecules across a partially permeable membrane from high to low water concentration
• Potato Osmosis Practical:

  1. Prepare multiple sucrose solutions from pure to highly concentrated
  2. Cut potato into same size pieces then divide into groups of three and weigh mass
  3. Place one group in each sucrose solution and leave it for 40 minutes
  4. Remove potatoes and dry them to remove excess water for a more accurate mass
  5. Potatoes gain mass in pure water as water is absorbed by osmosis
  6. Potatoes lose mass in highly concentrated sucrose as water concentration inside is higher